(1) Field of the Invention
The present invention relates generally to a system and method for ultraviolet disinfection and, more particularly, to a system and method for ultraviolet disinfection of drinking water.
(2) Description of the Prior Art
UV Mechanism of Action
It is well known in the art to use ultraviolet light (UV) for the disinfection treatment of water. Ultraviolet light, at the germicidal wavelengths, alters the genetic (DNA) material in cells so that bacteria, viruses, molds, algae and other microorganisms can no longer reproduce. The microorganisms are considered dead, and the risk of disease from them is eliminated. As the water flows past the UV lamps in UV disinfection systems, the microorganisms are exposed to a lethal dose of UV energy. UV dose is measured as the product of UV light intensity times the exposure time within the UV lamp array. Microbiologists have determined the effective dose of UV energy to be approximately about 34,000 microwatt- seconds/cm2 needed to destroy pathogens as well as indicator organisms found in water. Typical prior art disinfection systems and devices emit UV light at approximately 254 nm, which penetrates the outer cell membrane of microorganisms, passes through the cell body, reaches the DNA and alters the genetic material of the microorganism, destroying it without chemicals by rendering it unable to reproduce.
Ultraviolet light is classified into three wavelength ranges: UV-C, from about 200 nanometers (nm) to about 280 nm; UV-B, from about 280 nm to about 315 nm; and UV-A, from about 315 nm to about 400 nm. Generally, UV light, and in particular, UV-C light is xe2x80x9cgermicidal,xe2x80x9d i.e., it deactivates the DNA of bacteria, viruses and other pathogens and thus destroys their ability to multiply and cause disease, effectively resulting in sterilization of the microorganisms. Specifically, UV xe2x80x9cCxe2x80x9d light causes damage to the nucleic acid of microorganisms by forming covalent bonds between certain adjacent bases in the DNA. The formation of these bonds prevents the DNA codon from being read correctly for replication, and the organism is neither able to produce molecules essential for life process, nor is it able to reproduce. In fact, when an organism is unable to produce these essential molecules or is unable to replicate, it dies. UV light with a wavelength of approximately between about 250 to about 260 nm provides the highest germicidal effectiveness. While susceptibility to UV light varies, exposure to UV energy for about 20 to about 34 milliwatt-seconds/cm2 is adequate to deactivate approximately 99 percent of the pathogens.
Regulation of Drinking Water Standards
Exposure to pathogens does not always cause disease; whether drinking contaminated water could produce disease depends on the type and quantity of pathogen ingested and the health (nutritional and immunological) status of the person drinking the water. After studying certain variables, including the species and number of pathogens, the World Health Organization (WHO) has determined a standard of performance that must be met by acceptable water disinfection systems. The standard requires that an acceptable water disinfection system must be able to process contaminated water with 100,000 CFUs (colony forming units) of Escherichia coli (E. coli) per 100 ml of water and produce outlet water with less than one CFU per 100 ml.
United States Environmental Protection Agency (EPA) standards, as set forth in the National Primary Drinking Water Regulations (NPDWRs), have specific requirements for the levels of certain bacteria, protozoa, and viruses. Giardia lamblia, a protozoon, and all viruses must be 99.9% killed or inactivated. Heterotrophic microorganisms cannot exceed 500 colony-forming units (CFUs) per ml. No more than 5.0% of samples can be total coliform-positive in a month, and there can be no fecal coliforms present. Fecal coliforms and E. coli are bacteria whose presence indicates that the water may be contaminated with human or animal wastes. Microbes in these wastes can cause diarrhea, cramps, nausea, headaches, or other symptoms.
Prior Art
Typically, prior art devices and systems for disinfecting water via ultraviolet light exposure commonly employ standard ultraviolet light sources or lamps encased in quartz sleeves and suspended in the water being treated. Benefits of using ultraviolet light for disinfecting water include the following: no chemicals, like chlorine, are needed to ensure effective water disinfection provided that the proper number of lamps are used and properly positioned for a given influent and flow rate; since no chemicals are required in the disinfection process, no storage and/or handling of toxic chemicals is required; no heating or cooling is required to ensure disinfection; no storage tanks or ponds are necessary because the water can be treated as it flows through the system; no water is wasted in the process; no change in pH, chemical or resistivity of the water being treated; approximately at least 99.99% of all waterborne bacteria and viruses are killed via UV light exposure for disinfection; thereby providing increased safety of using the system and effectiveness of same.
As set forth in the foregoing, prior art UV water treatment systems disinfect and remove microorganisms and other substances from untreated, contaminated water sources and produce clean, safe drinking water. The core technology employed in WaterHealth International""s system includes a patented, non-submerged UV light. This technology is claimed by WHI to be a recent and tested innovation developed at the Lawrence Berkeley National Laboratory, a premier, internationally respected laboratory of the U.S. Department of Energy managed by the University of California. This prior art system delivers a UV dose of up to 120 mJ/cm2, which is more than three times the NSF International requirement of 38 mJ/cm2 and exceeds World Health Organization and EPA water quality standards and effectively treats bacteria, viruses and Cryptosporidium in drinking water. In addition, recent research conducted at two different laboratories indicates that UV doses of 10 mJ/cm2 or less produce 4-log reductions in Giardia. Based on this research, UV dosage of up to 120 mJ/cm2 greatly exceeds the dosage required for inactivation of Giardia. Additional components included in WaterHealth International""s systems effectively treat specific problems such as turbidity, silt, tastes, odors and various chemicals.
The UV light source used in prior art are typically low pressure mercury lamps, which can effectively clean water of dangerous and illness-causing viruses and bacteria, including intestinal protozoa such as Cryptosporidium, Giardia, and E. coli, provided that the proper number and configuration of lamps are included in the system.
Prior art UV disinfectant systems work best when the water temperature is between about 35 and about 110 degrees Fahrenheit, since extreme cold or heat will interfere with the UV system performance. Home temperatures are typically in this range.
Among applications for UV disinfection systems for water include the beverage industry, wastewater treatment, and surface treatment. By way of example and explanation, hot filled beverages, cold filled beer and other sensitive drinks are susceptible to contaminants introduced by the liners of closures. Mold is of particular concern since packaging headspace frequently contains low levels of oxygen. Medium pressure UV inactivates mold spores to prevent this problem, including contamination of beverages during production and storage, which can cause discoloration, unusual taste or bad flavor, and reduced shelf life. UV disinfection systems solve these issues by eliminating problem microorganisms without adding chemicals or heat. Disinfection of municipal water using UV light avoids problems associated with storage, transport and use of chemicals and associated regulation for them. Ultraviolet light can help improve shelf life of products and allow processors to reduce chemical additives in wash water without sacrificing high levels of disinfection. UV light provides non-chemical microbial control for captive water loops without altering the taste, color or odor of the food. Environmentally safe UV disinfection is one of the few water treatment methods unburdened by regulatory restrictions, consumer/environmental group concerns or high operation costs.
Problems Associated with Prior Art
Generally, UV disinfection is a safe and reliable means for disinfecting drinking water for daily use, particularly given its relatively rapid, inexpensive, non-taste and odorless resultant treated water. UV light is a World Health Organization-approved method of disinfecting drinking water (Guidelines for Drinking Water Quality, vol. 1, World Health Organization, Geneva, Switzerland, 1993, p. 135). However, UV disinfection is not generally recommended for long-term storage of water. Although UV disinfection will reduce pathogen levels to an acceptable level, a miniscule quantity of microbial contaminants may not be sterilized by the UV irradiation. Once the UV irradiation treatment is terminated, microbes that have survived the sterilization process may be able to replicate. Therefore, an ongoing disinfection system is required for longterm storage of water and other fluids. The most common means of maintaining water at an acceptable purity for long periods of time is through the addition of reactive chlorine. Unfortunately, evidence is mounting that organic chemical byproducts of chemical disinfection, especially byproduct of chlorination such as dioxane, are carcinogens and/or toxins for humans. Therefore, chemical disinfection is not a viable alternative when chemical purity of the fluid is desired and/or required. Additionally, in spite of this toxicological evidence, the EPA has recently been forced to relax restrictions on certain known carcinogenic chlorination by-product, such as chloroform. Additionally, other chemicals, such as the nitrate ion, have been shown to negatively influence the development of children.
In light of the emerging data concerning the toxicity of organic and inorganic chemicals and the relaxation of water purity regulations, persons interested in maintaining their health have been pursuing the supply of chemically pure water. Generation of such water requires filtration to remove the chemicals. Unfortunately, systems based on filtration require frequent replacement and/or cleaning of filters. In addition, storage of such water requires a system to maintain sterility for extended periods of time. Thus, there exists a need for a system that can easily remove or eliminate organic compounds from drinking water and maintain the sterility of that water during storage.
Current UV sterilization systems employ a submerged UV light system. Disadvantageously, a submerged UV light system requires cleaning and maintenance of the exterior of the system in order to protect the UV lamp or light source used in nearly all prior art systems. This cleaning can become a time-consuming duty, especially when working with multi-lamp low-pressure systems. During operation while the UV lamps and surrounding quartz sleeves are suspending in the water to be treated, minerals and contaminants in the water deposit onto the quartz sleeves, thereby causing fouling on the sleeve surface. This fouling reduces the effectiveness of the UV lamps because the fouling interferes with the UV light transmission into the water. To save time and prevent quartz sleeve fouling a cleaning mechanism can be supplied for either manual or automatic operation, like using wiper glides over the sleeves to remove deposits, which may block the light emitted from the UV lamp. This provides improved performance and reduces maintenance time, but only where the water quality is low. In every case, the UV lamps encased in quartz sleeves must be removed for cleaning on at least a monthly basis, depending on specifics of a given system and its influent and flow rates. The cleaning requires the system to be shut down temporarily or diverted to other UV lamps, so system shut down decreases capacity and/or increases operating costs. Also disadvantageously, UV lamps are susceptible to breakage, and if submerged, can contaminate the surrounding water. Commercially, only WaterHealth, Inc., might in any way suggest the use of non-submerged lamps for UV systems but these are limited expressly in advertising literature as applicable only and exclusively in applications that do not require high purification, e.g., previously purified drinking water but not surface water, aquifer water, wastewater, or otherwise unpurified water treatment applications.
These prior art systems do not employ optical components nor reflective materials or photocatalytic materials in the holding tank and reaction vessels.
Thus, there remains a need for a UV disinfection system for treating fluids having reduced maintenance time and costs, increased flow rates for a given disinfection level, lower overall equipment, installation, and system costs, reduced risk of fluid contamination by equipment breakage, and capable of maintaining the sterility of fluids for extended storage periods. Additionally, there remains a need for water purification system that can remove or degrade organic compounds and other chemical contaminants in fluids with reduced maintenance.
The present invention is directed to a UV disinfection system and method for treating fluids, particularly water, whereby the UV light source requires less maintenance and cost than prior art systems and devices while providing at least the same disinfection level for a given influent and flow rate thereof.
One object of the present invention is to provide a UV disinfection system for treating fluids configured and arranged to function effectively with at least one UV light source or lamp that is not submerged in the fluid to be disinfected. The UV light source is positioned outside the fluid to be disinfected via exposure to at least one UV dose zone wherein UV light is projected into the zone.
Another object of the present invention includes presentation of the UV light source presented in at least two primary configurations: a vertical riser configuration and a non-riser, holding tank configuration. In the vertical riser configuration the UV light source is positioned above the fluid to be treated and projecting a UV dose zone downward toward and into the fluid to be treated, with the fluid moving upward toward the UV light source. Alternatively or in series combination with the vertical riser configuration, the UV light source maybe presented in a non-riser, holding tank configuration, wherein the UV light source is positioned above the fluid holding tank or other container to be treated and projecting a UV dose zone downward toward and into the fluid to be treated, with the fluid in a substantially static or non-moving conditions.
Still another object of the present invention is to provide a UV dose zone including at least one zone, more preferably four zones, wherein one zone includes an interface zone positioned between the UV light source and the fluid to be treated and another zone includes a reaction zone positioned within the fluid. The reaction zone may be formed by an interface plate that incorporates catalytic properties to enhance desired reactions.
The present invention is further directed to a method for treating fluids by disinfecting those fluids using UV light projected by at least one UV light source producing at least one dose zone, the UV light source being positioned outside the fluid.
Accordingly, one aspect of the present invention is to provide a system and method for disinfecting fluid including at least one UV light source positioned outside the fluid to be treated with the at least one UV light source producing at least one UV dose zone for disinfecting the fluid, wherein the fluid is water, preferably water that has been previously treated for sterilization and/or disinfection.
Another aspect of the present invention is to provide a system and method for disinfecting and purifying fluid including at least one UV light source positioned outside the fluid to be treated with the at least one UV light source producing four UV dose zones for disinfecting the fluid, with one zone provided at an interface zone, and one zone provided at a reaction zone positioned between the UV light source and the fluid to be treated. The reaction zone may be formed by an interface plate that incorporates catalytic properties to enhance desired reactions
Still another aspect of the present invention is to provide a system and method for disinfecting fluid including at least one UV light source positioned outside the fluid to be treated with the at least one UV light source producing at least one UV dose zone for disinfecting the fluid, wherein the at least one UV light source is a medium-to-high intensity UV light source or spectral calibration lamp. These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment according to the present invention when considered with the drawings.